Thanks for your article, I have followed it through and I think there may be a couple of typos in your formula....
h25 - Should this read....
( COUNTROWS ( 'Measures' ) - 1 ) * 0.25 + 1,
FILTER ( 'Measures', [FilterColumn] = [FilterCondition] )
x25up - Is this missing a MAXX function?
I think that's all I picked up.
I am still working through my data, so will post back once I am done.